justyo

Yo (justyo.co) was a single-tap notification app and "the world's simplest API." A service registered an API username, received an api_token, and could push a lightweight "Yo" notification to a single subscriber or broadcast to all subscribers, optionally attaching a link, plus read the subscriber count. The Yo API had effectively one job — fire a push — with an api_token for auth (an OAuth 2.0 page was documented but never enabled) and first-party client SDKs across Python, PHP, Java, Node, Ruby, Scala and iOS under the github.com/YoApp organization. The Yo service is now defunct: the justyo.co host is suspended and its api/docs/dev subdomains no longer resolve. This API Evangelist profile captures the historical Yo API surface for the record.

justyo publishes 2 APIs on the APIs.io network: Account API and Yo API. Tagged areas include Company, Notifications, Push Notifications, Messaging, and Mobile.

justyo’s developer surface includes documentation, signup flow, authentication, and 12 more developer resources.

🌐 Visit website 📡 Source on GitHub
37.2/100 thin ▬ flat Agent 54/100 agent ready Full breakdown ↓
scored 2026-07-27 · rubric v0.5
AccessSelf serve
2 APIs 1 MCP Servers
CompanyNotificationsPush NotificationsMessagingMobileDeveloper ToolsAPI

Kin Score

Kin Score Kin Score How this is scored →
scored 2026-07-27 · rubric v0.5
Composite quality — 37.2/100 · thin
Contract Quality 14.6 / 25
Developer Ergonomics 10.0 / 20
Commercial Clarity 2.6 / 20
Operational Transparency 0.7 / 13
Governance 0.0 / 12
Discoverability 9.3 / 10
Agent readiness — 54/100 · agent ready
Machine-Readable Contract 18 / 18
Agentic Access Contract 0 / 15
MCP Server 12 / 12
Machine-Readable Auth 10 / 10
Idempotency 0 / 9
Stable Error Semantics 0 / 8
Request/Response Examples 0 / 7
Rate-Limit Signaling 7 / 7
Typed Event Surface 0 / 6
Agent Skills 5 / 5
Well-Known Catalog 4 / 4
Consent & Bot Identity 0 / 3
Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. This rating is computed from github.com/api-evangelist/justyo: open an issue to ask a question, or submit a pull request to add artifacts. Want it done for you? Prioritized profiling — $2,500 →

APIs 2

Individual APIs this provider publishes, each with its own machine-readable definition.

justyo Account API

Read account/subscriber information.

justyo Yo API

Send Yo notifications to subscribers.

MCP Servers 1

Model Context Protocol servers that expose these APIs to AI agents.

justyo-mcp.yml

MCP SERVER

Rate Limits 1

Documented rate limits and quota policies.

Justyo Rate Limits

0 limits

RATE LIMITS

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Justyo Authentication

apiKey · 1 scheme

SECURITY

Justyo Domain Security

no transport/DNS hardening detected

SECURITY

Resources

Get Started 2

Portal, sign-up, and the first successful call

DeveloperPortal
DeveloperPortal
 SignUp
SignUp

Documentation 1

Reference material describing how the API behaves

Documentation
Documentation

Agent Surfaces 4

MCP servers, agent skills, and machine-readable catalogs

MCPServer
MCPServer
 LLMsTxt
LLMsTxt
 WellKnown
WellKnown
 AgentSkill
AgentSkill

Design & Contract 2

Pagination, idempotency, versioning, errors, and events

Conventions
Conventions
 Lifecycle
Lifecycle

Build 3

SDKs, sample code, and the tooling you integrate with

GitHubOrganization
GitHubOrganization
 Packages
Packages
 SDKs
SDKs

Access & Security 2

Authentication, authorization, and security posture

Authentication
Authentication
 DomainSecurity
DomainSecurity

Company 1

The organization behind the API

Website
Website

Source (apis.yml)

apis.yml Raw ↑ 
aid: justyo
name: justyo
description: 'Yo (justyo.co) was a single-tap notification app and "the world''s simplest API." A service registered an API
  username, received an api_token, and could push a lightweight "Yo" notification to a single subscriber or broadcast to all
  subscribers, optionally attaching a link, plus read the subscriber count. The Yo API had effectively one job — fire a push
  — with an api_token for auth (an OAuth 2.0 page was documented but never enabled) and first-party client SDKs across Python,
  PHP, Java, Node, Ruby, Scala and iOS under the github.com/YoApp organization. The Yo service is now defunct: the justyo.co
  host is suspended and its api/docs/dev subdomains no longer resolve. This API Evangelist profile captures the historical
  Yo API surface for the record.'
url: https://raw.githubusercontent.com/api-evangelist/justyo/refs/heads/main/apis.yml
x-type: company
x-source: vc-portfolio
x-backed-by:
- slow-ventures
x-tier: stub
x-tier-reason: portfolio-lead
x-status: defunct
accessModel:
  pricing: unknown
  onboarding: self-serve
  trial: false
  try_now: false
  public: false
  label: Self-serve signup
  confidence: medium
  source:
  - authentication
  generated: '2026-07-22'
  method: derived
specificationVersion: '0.20'
created: '2026-07-17'
modified: '2026-07-19'
image: https://raw.githubusercontent.com/api-evangelist/justyo/refs/heads/main/openapi/justyo-yo-openapi.yml
tags:
- Company
- Notifications
- Push Notifications
- Messaging
- Mobile
- Developer Tools
- API
apis:
- aid: justyo:justyo-account-api
  name: justyo Account API
  description: Read account/subscriber information.
  humanURL: https://docs.justyo.co/
  baseURL: https://api.justyo.co
  tags:
  - Account
  properties:
  - type: OpenAPI
    url: openapi/justyo-account-api-openapi.yml
  - type: Authentication
    url: authentication/justyo-authentication.yml
  - type: RateLimits
    url: rate-limits/justyo-rate-limits.yml
  - type: ErrorCatalog
    url: errors/justyo-problem-types.yml
  - type: DataModel
    url: data-model/justyo-data-model.yml
  - type: Conventions
    url: conventions/justyo-conventions.yml
- aid: justyo:justyo-yo-api
  name: justyo Yo API
  description: Send Yo notifications to subscribers.
  humanURL: https://docs.justyo.co/
  baseURL: https://api.justyo.co
  tags:
  - Yo
  properties:
  - type: OpenAPI
    url: openapi/justyo-yo-api-openapi.yml
  - type: Authentication
    url: authentication/justyo-authentication.yml
  - type: RateLimits
    url: rate-limits/justyo-rate-limits.yml
  - type: ErrorCatalog
    url: errors/justyo-problem-types.yml
  - type: DataModel
    url: data-model/justyo-data-model.yml
  - type: Conventions
    url: conventions/justyo-conventions.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: Website
  url: https://justyo.co
- type: Documentation
  url: https://docs.justyo.co/
- type: DeveloperPortal
  url: http://dev.justyo.co/
- type: GitHubOrganization
  url: https://github.com/YoApp
- type: SignUp
  url: https://dashboard.justyo.co/
- type: Packages
  url: packages/justyo-packages.yml
- type: SDKs
  url: packages/justyo-packages.yml
- type: MCPServer
  url: mcp/justyo-mcp.yml
- type: LLMsTxt
  url: llms/justyo-llms.txt
- type: WellKnown
  url: well-known/justyo-well-known.yml
- type: Authentication
  url: authentication/justyo-authentication.yml
- type: Conventions
  url: conventions/justyo-conventions.yml
- type: Lifecycle
  url: lifecycle/justyo-lifecycle.yml
- type: DomainSecurity
  url: security/justyo-domain-security.yml
- type: AgentSkill
  url: skills/_index.yml
x-enrichment:
  date: '2026-07-19'
  status: backfilled
  pass: local-v1
  note: backfilled from .gitignore signal + verified work evidence